This invention relates to gripper apparatus for engaging work pieces for processing. The principles of this invention are applicable to the gripping of work pieces of many types either internally or externally. But in particular this invention is uniquely suitable for the suspension of tools from the tube sheet of a steam generator, which is to be sleeved, by gripping of neighboring tubes internally as described in Arzenti. In the interest of relying on a concrete embodiment in the explanation of this invention, this invention is described as applied to the suspension of tools from the tube sheet of a steam generator. To the extent that this invention is applied to the processing of work pieces of other types than tube sheets, whether the work pieces is gripped internally or externally, such application is within the scope of equivalents of this invention.
The tubes of a steam generator which carry the hot fluid whose energy (enthalpy) is converted into steam by heat exchange are sealed through the tube sheet. In case of a steam generator of a nuclear reactor plant, these tubes carry the coolant heated by the core of the reactor. A channel head extends downwardly from the periphery of the tube sheet. The hot fluid enters an inlet section of the channel head, is conducted through the tubes to an outlet section and out of the outlet section. In case of a steam generator of a nuclear reactor plant, the coolant is radioactive and the channel head is radioactive.
It has been found that the tubes of a steam generator which conduct the coolant become corroded or damaged in other ways and must be sleeved. The sleeving is effected by a succession of tools which are suspended from the tube sheet. Since the reactive forces generated by the tools in performing their functions are high, the tools must be firmly and reliably suspended from the tube sheets. This is a particularly urgent requirement in the case of a steam generator of nuclear-reactor plants where the tube sheet and the channel head are radioactive.
It is an object of this invention to provide gripper apparatus for firmly and reliably suspending such tools.
The suspension of the tools is effected, separately for each tube to be sleeved, by gripper apparatus provided on the mountings of the tools. The gripper apparatus has gripper means which penetrates into tubes adjacent to a tube to be sleeved and firmly grips these neighboring tubes. Such gripper apparatus is sometimes referred to as a camlock. The neighboring tubes include intact tubes which require no sleeving, corroded or damaged tubes which may later require sleeving and sleeved tubes. The inside diameter of a sleeved tube is substantially smaller than the inside diameter of an unsleeved tube. It is accordingly necessary that the gripper means of the gripper apparatus be operable over a substantial range so that it may grip reliably both sleeved and unsleeved tubes.
Gripper apparatus in accordance with the teachings of the prior art includes a collet within which there is longitudinally movable mandrel. The collet includes prongs or keys which are held in retracted position by O-rings. When the mandrel is to engage work, the mandrel is retracted expanding the collet to engage the work. One difficulty with this prior art gripper apparatus is that the range of the collet between the open and closed positions is limited. Such gripper apparatus which is suitable for engagement with a sleeved tube cannot serve for engagement with an unsleeved tube and vice versa. It is then necessary to interchange gripper apparatus, in the radioactive environment of the channel head, in dependence upon whether a sleeved tube or an unsleeved tube is to be engaged. In addition one or more of the keys sometimes protrudes and is thrust against the end of the tube when an attempt is made to insert the collet. Also, the O-rings have a limited life.
Typical prior art is also disclosed in Groves U.S. Pat. No. 3,698,756. Groves is complicated in its structure and operation and because of its complexity is unreliable. In Groves a plunger rod urges flexible fingers into engagement with work and a sleeve is slidable by the plunger rod through a pin to disengage the fingers from the work. Misalignment of the pin would cause bending and jam this gripper apparatus.
It is accordingly an object of this invention to provide reliable gripper apparatus of uncomplicated structure and operation having a wide range such that the same unit of apparatus can be used to suspend processing tools both from sleeved tubes and from unsleeved tubes. It is also an object of this invention to provide a method for operating such apparatus.